A mixer head of this type is marketed by Process Systems, Inc., Park Ridge, Ill., under the registered trade name Scott Turbon Mixer. This mixer head has a mixing chamber comprising two sections in the form of truncated cones; one at each end of a cylindrical middle section which is slotted along its periphery, and a central shaft extends through the mixer head. The conical sections act as centrifugal pumps pumping the substances to be mixed into the cylindrical section where in a first stage they undergo a hydraulic shear where the two streams meet. The slots in the middle section act in a second stage as specific shear elements, while a third shear stage occurs when the radial discharge from the head meet the slower moving contents of the mixing vessel. The shear forces act to mix the substances and in particular to disperse and dissolve solids in the fluid mixture.
Mixer heads of this type present several disadvantages. Thus, for a given diameter of the mixing chamber and a given rotational speed the throughput is delimited by the smaller cross sectional inlet areas of the conical sections. Further, in acting as centrifugal pumps the conical sections impart to the substances to be mixed a considerable tangential component of velocity which rather than to contribute to the hydraulic shear detracts therefrom. The central shaft extending through the mixing chamber reduces the volume thereof and thereby the retention time therein for the fluid mixture. Finally such mixer heads are not immediately accessible for ocular inspection after a cleaning-in-place procedure (CIP-procedure) due to the presence of the conical sections and the throughgoing shaft.